Heretofore, as a fuel gas for the fuel cells, the reformed gas, which is obtained through steam reforming of hydrocarbon such as methane, propane or so in natural gas, alcohol such as methanol, naphtha or the like, has been widely used from an aspect of the cost. The reformed gas of this kind contains carbon monoxide in addition to hydrogen, carbon dioxide or so, it has been known that approximately 1 vol. % of the carbon monoxide is contained even after processing by shift reaction.
Although the secondary produced carbon monoxide of this kind is applied as also fuel in high-temperature working type fuel cells such as a molten carbonate fuel cell (MCFC), the carbon monoxide it has a catalytic poison effect on platinum-based catalysts as the electrode catalysts in a low-temperature working type fuel cells such as a phosphoric acid fuel cell (PAFC) and the polymer electrolyte fuel cell, the catalyst poisoning caused by the carbon monoxide co-existing in the reformed gas is remarkable and a problem of deterioration in generation efficiency arises especially in the polymer electrolyte fuel cell, which is operated in lower temperature as compared with the phosphoric acid fuel cell.
Heretofore, in order to cope with the problem of this kind, alumna catalysts applied with various platinum metals have been proposed.
However, selectivity and activity of the oxidation reaction by oxygen are low in the alumna catalysts applied with such the platinum metals, therefore there is another problem in that hydrogen, which is the main component of the reformed gas and reacts as fuel gas, is also oxidized and dissipated at the same time, thereby causing degradation of utilization factor of the fuel.
Furthermore, it is necessary to supply the reformed gas after reducing the co-existing carbon monoxide into a hundredth of the original amount of approximately 1 vol. % or below in order to obtain the required generation efficiency by using the reformed gas in the polymer electrolyte fuel cell, but the carbon monoxide is not reduced sufficiently by the conventional platinum-alumna based catalysts, and deterioration of the generation efficiency is caused by the remaining carbon monoxide.